In oil wells and other similar applications in which the production of fluids is desired, a variety of fluid lifting systems have been used to pump the fluids to surface holding and processing facilities. It is common to employ various types of downhole pumping systems to pump the subterranean formation fluids to surface collection equipment for transport to processing locations. One such conventional pumping system is a submersible pumping assembly which is immersed in the fluids in the wellbore. The submersible pumping assembly includes a pump and a motor to drive the pump to pressurize and pass the fluid through production tubing to a surface location. A typical electric submersible pump assembly (“ESP”) includes a submersible pump, an electric motor and a seal section interdisposed between the pump and the motor.
Centrifugal well pumps are commonly used as the submersible pump in an ESP application to pump oil and water from oil wells. Centrifugal pumps typically have a large number of stages, each stage having a stationary diffuser and a rotating impeller driven by a shaft. The rotating impellers exert a downward thrust as the fluid moves upward. Also, particularly at startup and when the fluid flow is non-uniform, the impellers may exert upward thrust. It is most common for the impellers to float freely on the shaft so that each impeller transfers downward thrust to an adjacently located diffuser. Thrust washers or bearings are often located between each impeller and the upstream diffuser to accommodate the axially directed upward and/or downward thrusts.